This invention relates to the preparation of compatible blends of polyarylene sulfide and epoxy-functionalized siloxane polymers and, more particularly, to the preparation of polyphenylene sulfide/epoxy-functionalized siloxane blends.
Polyarylene sulfides are crystalline engineering thermoplastics with high crystalline melting temperatures, typically on the order of 285.degree. C., and are characterized by low flammability, high modulus, and excellent resistance to aggressive chemicals and solvents. However, their glass transition temperatures are very low, typically as low as 85.degree. C. As a consequence, heat distortion temperatures are low in the absence of reinforcement with fillers such as glass fiber. In addition, polyarylene sulfides are very brittle, as evidenced by a tensile elongation for poly-phenylene sulfide usually no greater than about 2.5% and frequently below 1%. Typical characteristics include high flexural modulus, low elongation, and poor impact strength. The non-reinforced resin is commonly used in coatings.
A new market segment for PPS is automotive. While PPS has been used for automotive engine sensors and halogen lamp sockets, it has not been used for major components. Now that engine compartments are getting smaller, while performance requirements are getting higher, under-the-hood temperatures could go as high as 340.degree. F. Past 1995, temperatures are foreseen at above 400.degree. F. As temperatures increase, the contact with engine oil, fuels, gasoline, antifreeze, transmission fluid, and brake fluid become more critical for commonly used under-the-hood plastics. Because of the chemical resistance and high heat advantage of PPS, it is being considered for fuel systems, manifolds, and valve covers. The tensile strength for PPS is typically 20-27.7 at 1000 psi (ASTM D-638). The flexural strength is typically about 26-39.8 at 1000 psi, and the flexural modulus is typically about 1.7-2.2 at 10.sup.6 psi (ASTM D-790). Heat-deflection temperatures of 500.degree. F. are typical, as well.
To enhance heat resistance and impact properties, polyarylene sulfide is often blended with other polymers such as polyphenylene ethers, as disclosed in U.S. Pat. No. 5,122,578 :,Han et. al.), the disclosure of which is incorporated by reference herein for typical reagents and conditions employed in the preparation of functionalized polyarylene compounds. However, it has been recognized that blends of polyarylene sulfides with other resins often undergo phase separation and delamination because the two resins are incompatible, and there is little or no phase interaction between the two resin phases. Molded parts made from such incompatible blends are typically characterized by low tensile and impact strength. Blends of polyarylene sulfides and siloxanes have provided improved impact properties. However, further improvements in impact properties and temperature resistance are desired.